The propensity of synthetic fibers to develop a static charge is a well known phenomenon. Static electricity is generated when two relatively non-conducting surfaces, such as those of synthetic fibers, come into close contact and are rubbed together. This leads to a continuous flow of electrons in both directions across the two surfaces. On separation the electron distribution on the surfaces is disturbed; one surface retaining more electrons than in its normal state acquires a negative charge and the other an equivalent positive charge.
Static can be controlled by eliminating the charge generation or by increasing the rate of charge dissipation. Due to the hydrophobicity of synthetic fibers, the synthetic fibers are not able to dissipate the generated electricity. Most anti-static treatments attempt to increase the hygroscopicity, (i.e. the ability of fibers to adsorb moisture from the air), to increase the rate of charge dissipation.
Anti-static treatments for synthetic fibers and fabrics generally include spray-on treatments applied to fibers after the fiber is extruded or to fabrics, after the fabric is woven or knitted.
For synthetics or polymeric materials, such as polyamide, anti-static treatment may also be achieved by mixing large quantities (20%-50%) of an anti-static agent with caprolactam in a polymerization vessel during the polymerization reaction of polyamide to produce a "master batch" of polyamide containing anti-static agent. The anti-static polyamide fiber is then produced by blending the "master batch" with virgin polyamide chips in a blender or tumbler.
However, this method has serious drawbacks as the concentration of anti-static agent is batch dependent and varies according to the requirements of the specific batch. The anti-static containing polyamide chips of the "master batch" do not blend uniformly with the virgin polyamide and the anti-static properties of the extruded fiber are not uniform. Also, this anti-static treatment to polyamide requires elaborate and expensive spinning equipment to control or regulate the rate of addition of anti-static agent. Examples of such equipment include side arm extruders and colortronics.
The present invention provides a method for addition of an anti-static agent to molten polymeric material contained in a spinning extruder without the use of equipment such as a side arm extruder. According to the method of the present invention, an anti-static agent that is solid at room temperature, is melted and added to the molten polymeric material. The method is an improvement over the prior art, as it provides an accurate and efficient method for addition of an anti-static agent to a spinning extruder, without the use of expensive equipment.
Unexpected results are achieved when fibers or fabrics are treated with the anti-static agent according to the present invention. These unexpected advantages include improved stability of the fabric to ultraviolet light, significantly improved dye lightfastness and improved dye uptake, resulting in deeper dyeing, in comparison to untreated control samples.